1. Field of the Invention
The present invention relates to an optical memory element on which a laser beam is impinged to record, read out or erase the information onto or from the optical memory element. The present invention relates, more particularly, to a dual-surface optical memory disc including separate two optical memory elements.
2. Description of the Prior Art
Recently, an optical memory system has been developed, which optically stores the information in high density and in the mass storage order. Especially, the optical memory disc will be widely utilized because the optical memory disc ensures a rapid access to the desired information. A dual-surface (double-sided structure) optical memory disc is proposed in a copending U.S. patent application Ser. No. 638,674, "OPTICAL MEMORY DISC", filed on Aug. 8, 1984, and assigned to the same assignee as the present application. The dual-surface optical memory disc is effective to increase the memory capacity on one optical memory disc.
However, in the conventional dual-surface optical memory disc such as proposed in the U.S. patent application Ser. No. 638,674, the thickness of the optical memory disc is not accurately controlled. Therefore, the rotating condition of the conventional dual-surface optical memory disc is not always stable.